1. Field of the Invention
This invention relates generally to sewage treatment systems and more specifically to an improved method and apparatus for treating domestic sewage in environmentally sensitive rural areas.
2. Description of the Prior Art
Treatment of domestic sewage is a perpetual problem for rural single family dwellings and small housing developments due to the necessity of maintaining safe, healthful environments and drinking water with only limited funds available to do so. Towns and cities have been able to treat sewage economically by utilizing taxes and fees collected from larger bases of industries, businesses, and individuals to provide common municipal treatment systems for entire communities. Because of such larger taxpayer and user bases, such municipal systems can be designed and constructed with varying degrees of sophistication, depending on the nature of the sewage produced, and provided with a staff of trained, professional operators, to meet stringent sewage treatment standards promulgated by governmental regulatory agencies. Further, in order to maintain a healthful environment and to preserve the safety of water resources, such standards have been made more stringent in recent years.
Unfortunately, such expensive, sophisticated sewage treatment facilities are not practical or feasible for rural single family dwellings or small housing developments. Yet, it is just as important to maintain health and safety standards in rural areas as it is in urban areas. To compound the problem, it is the desire of more and more people to construct their houses in rural and mountainous areas, which are aesthetically pleasing, but which unfortunately are also usually more environmentally sensitive. Mountainous areas in particular typically have relatively thin top soil layers over impervious rock substructures. Therefore, such soils have only very marginal capacity for absorbing wastewater and retaining it for sufficient periods to allow a natural purification process to be accomplished.
The conventional approach to domestic sewage systems in rural areas over the past several decades has been to empty the raw sewage into an anaerobic septic tank where anaerobic bacteria digest the sewage, breaking down solids and consuming some nitrates and nitrites in the process. Some sediment or sludge settles to the bottom of the septic tank, and liquid effluent overflows into an underground drain field where it seeps into the ground there is limited B.O.D., T.S.S., coliform bacteria, or phosphate treatment in such primary septic tank treatment, and the nitrogen treatment is inadequate. In rural agricultural areas where population densities are low and where top soil and subsoil layers are usually quite deep and sufficiently permeable to adsorb and retain the liquid effluent from septic tanks, such conventional septic systems have been satisfactory. With enough capacity and long enough retention time, the oxygen and bacteria in the soil eventually break down and treat the primary sewage components to safe levels.
However, in more environmentally sensitive areas, such as the desired mountainous home sites described above, it is now generally accepted that conventional primary septic system treatment is clearly inadequate. With thin layers of topsoil over impervious bedrock, the incompletely treated liquid effluent from a septic tank can easily pass essentially unaltered into the ground water or can surface and trickle as run-off into open streams, ponds, and lakes. Further, the untreated effluent can follow cracks and fractures in the bedrock to underground aquifers, thus fouling wells and water supplies of the residents in the area. Also, it has become more clear in recent years that substantial amounts of nitrogen and phosphorus are contained in domestic sewage. These components are damaging to the environment but are not effectively removed by conventional septic systems and can remain in the effluent to enter ground and surface waters. Therefore, while pressure to build houses in such rural, environmentally sensitive areas is increasing, the pressure on the environment is increasing even more rapidly. Some state and local governments are working to develop more stringent sewage treatment standards for such areas that conventional septic systems cannot meet and are even prohibiting further home building where there are no other sewage treatment alternatives available.
There have been some recent developments in improving septic tank systems. For example, the following U.S. patents utilize multiple-cell septic tanks and incorporate aerobic then anaerobic sequential treatment: U.S. Pat. No. 1,331,735, issued to J. Wilson; U.S. Pat. No. 3,930,998, issued to P Knopp et. al.; U.S. Pat. No. 4,374,730, issued to A. Braha et. al.; and U.S. Pat. No. 4,246,099, issued to M. Gould et. al. Further, the U.S. Pat. No. 4,279,753, issued to N. Nielson et. al. discloses an anaerobic/arobic/anaerobic/ then tertiary sequence. The U.S. Pat. No. 3,202,285, issued to F. Williams shows an anaerobic tank that separates sewage by densities followed by an aerobic tank. The U.S. Pat. No. 4,325,823, issued to Graham also shows an anaerobic/aerobic/settling tank sequence.
Other improvements have also been made in septic systems. For example, the U.S. Pat. No. 4,279,753, issued to Nielson et. al. discloses the use of alum to precipitate phosphates and a plurality of vertical plastic sheets in the aerobic tank to increase surface area for growth of aerobic microorganisms. The U.S. Pat. No. 3,930,998, issued to Knopp et. al. also discloses the use of methanol to support anaerobic bacteria.
While all of these innovations have been improvements to some extent over the conventional septic tank systems, none of them have been effective to achieve sufficient primary and secondary treatment of all the B.O.D., T.S.S., nitrogen, phosphate, and coliform bacteria components of the sewage to render it safe for such environmentally sensitive areas as described above. Therefore, in order for an individual or small group of persons to build homes on such environmentally sensitive sites, there was still, prior to this invention, an increasingly urgent need for a relatively small and inexpensive domestic sewage treatment system that could accomplish both primary and secondary treatment of all the B.O.D., T.S.S., nitrogen, phosphate, and coliform bacteria components to environmentally safe standards and which would be relatively easy and inexpensive to maintain over long periods of time.